What attributes to the most aggressive spiral wound channels? Do longer heads spiral more. Shorter wider heads? Degree of bevel? Has there been study of this? Personal observations?
Bishop Archery says that their 630 grain head has more spiral than any other...I think probably due in part to the thickness of the blade. In my mind, a steeper bevel (40 degrees vs the more common 25 degrees) coupled with a thicker that average blade helps with a more aggressive spiral. Btw, the only other single bevel broadhead that I know of besides the Bishops that has 40 degree bevels is the Helix by Strickland...which is also well known for it's spiral effect and interior carnage.
:scared: those bishop BH's look killer...on my wallet!!
:knothead: I don't understand going to all that trouble in making such a bombproof BH then making it a screw in which incorporates a weak link such as the shank of a screw in head. Make it a glue on and mount it to a glue on/glue in adapter. Many times stronger especially, when footed with alloy arrow.
it would seem to me that a narrower head would spin at a faster rate than a wider head.
You got me thinking about that, Chuck. Trying to ride the arrow in my brain. :)
Borrow an arrow with a wide head and one with a narrow head and run each thru a raw potato ( large one) or a squash or small watermelon See what they do.
Then report back to us !
The key is to have the head continue to turn the same direction the arrow is turning. If you mix them the head will actually stop and try and reverse the direction on impact.
Mike
So do we want penetration or spiraling? The more rotation the less penetration.
I think penetration.
I like wensels and sharks for whitetails. Those Badgers and Cutthroats look wicked to me. 5 years ago i shot a doe quartering hard away. I shot her with a 52lb centaur and sharp grizzly. That arrow went through the ham on my side and through every organ and out the off side scapula! I will also attest, shooting foam targets with single bevels seam to dice up target more than double bevels i shot.
I am far from an expert in physics but just a thought here... if encountering soft tissue such as muscle I would imagine more spiraling would decrease penetration some. However, when encountering hard bone, more rotation could give a great chance to split the bone, thus increasing penetration.
I think sometimes we think too much. My thoughts are, use a good sharp head on a bow / arrow set up that will deliver two holes most times, then put it in the right place. Dead is dead. Single bevels are great but so are double bevels and three blade heads. Get em sharp, make a special delivery, and it will work out. Usually
This is just my opinion, but I think that with a single bevel bh penetration equals spiral/rotation. Its when the single bevel meets resistance as it penetrates that cause or pushes the bh to rotate. Im pretty sure I read something about that from all of Dr. Ashby's stuff.
the angle of the bevel would have greatest effect on the degree of rotation, just as the pitch of a boat propeller.
Quote from: ozy clint on May 08, 2018, 06:45:13 AM
the angle of the bevel would have greatest effect on the degree of rotation, just as the pitch of a boat propeller.
I agree. That's why in my opining its best to make sure that bevel is true through out the length of the BH. Not all single bevel bh are created equal. A lot of them have a narrower bevel than others. Which I feel effects rotation. Might not be much but I feel it does. I think Dr. Ashby called Mechanical Action or MA
On a propeller ( water) the two sales features are pitch and size of blade, the latter kinda morphing into diameter as well as number of blades for surface area. Does that translate ? Does it really matter if the thickness or pitch remain constant along its entire contact length as long as the leading edge, maybe one third, has the driving force to start and maintain the twist ? and finally.....does D O G really spell.....CAT ?
Ashby's MA reference is to "mechanical advantage" which is the term he used to describe the advantage of a 3/1 ratio. IOW, no matter how sharp the steak knife or how tender the steak it's always easier to cut by drawing the blade through at an angle as opposed to the opposite of trying to press the blade straight down.
Pretty interesting video here. This is what got me wondering, along with the multiple designs now marketed.
https://youtu.be/u6BLX3zlJkk
To answer your question...Centaur Big Game Head.
Wide and thick steel.
Tedd
This is what a Badger looks like going though gel. [attachment=1]
oops, guess I will have to do some research to figure out how to load this video.
I saw that video and it was impressive just need them heavier for my set up.
I believe the thickness of the blade and bevel has more influence.
Abowyer spins pretty quick at impact but I would think it doesn't really matter :biglaugh:
i was thinking today about the effect of what is termed 'blade pitch distribution'. pitch distribution is the change in pitch along the length of a propeller blade. closer to the rotational axis the blade has a higher pitch because it doesn't travel as far per rotation than the tips of the blade where the pitch is less. this allows the blade to create more equal thrust along any given point of it's length.
transfer this principle to broadheads and you soon realize that broadheads don't have any change in pitch distribution between the part of the blade close to the rotational axis (the tip of the broadhead) and the part furthest from the axis (the rear of the blade at it's widest point)
whether this is a good or bad thing i'm not sure. it would be bad for a propeller meant to create thrust from rotational energy (aircraft and boat propellers) and a turbine meant to create rotational energy from thrust (steam turbine) as it would be very inefficient.
i was thinking perhaps it is a good thing since when a BH is passing through flesh the wider part of the blade would have greatest effect on the speed of rotation meaning the tip of the blade would effectively be spinning faster than the pitch (bevel angle) would otherwise cause it to rotate. this perhaps creates tension on the flesh passing over the blade edge allowing the edge to cut it more easily.
just some thoughts i had...............
I shoot Abowyer single bevel heads and like them a lot. I think width probably contributes the most towards the spiraling effect. Most broadheads have ground edges that are about the same angle so I would think the difference there would be minimal.
Quote from: MnFn on May 06, 2018, 11:36:57 AM
I think penetration.
Actually,that's exactly what doesn't happen.That's been tested to death.The spreading of the soft tissues by the bevels,evidently relieves pressure and allows the arrow to penetrate better.That's why in Doc Ashby's tests,identical broadheads,one with double bevel and the other single bevel,the single bevel penetrated substantially farther.That's the whole point.
I've used a couple different single bevels but of similar dimensions.In a consistent target medium,they turn,1/4 turn in 4",consistently.Doc Ashby talks about a full turn in 16".That seems to be what I'm seeing.I've only shot a few head of big game with them but wound channels for a 1 3/16" broadhead were 2" wide,in soft tissue.
I'm not sure you will see a lot of difference in rate of twist among different single bevel broadheads.I personally like to use broadheads that are of a 3 to 1 ratio,when I can,to also help with penetration.
If I knew how to post pictures I would show you what a single bevel can do to a deer thigh bone shot from a 46 lb long bow. I was waiting for her to look the other way before shooting when she raised her hind leg to scratch her head. The shot went thru her body and into that raised leg. What it did to that leg was amazing & sold me on single bevels. I couldn't believe what I saw when I started butchering the deer.
Jim